President Trump’s lawyer Rudolph W. Giuliani said Tuesday that Trump will not agree to an interview with the special counsel until prosecutors allow the president’s legal team to review documents related to the FBI’s use of a source to interact with members of Trump’s 2016 campaign.

“We need all the documents before we can decide whether we are going to do an interview,” Giuliani said in an interview with The Washington Post, using Trump’s term “spygate” to refer to the FBI actions, which former officials have said were well within bounds.

Giuliani’s latest demand further ratcheted up the pressure that Trump and his lawyers are trying to place on special counsel Robert S. Mueller III’s team as his investigation into alleged coordination between Trump’s campaign and Russia reaches a key juncture.

Earlier Tuesday, Trump lashed out at the “Rigged Russia Witch Hunt” on Twitter, casting Mueller’s probe as partisan and saying it could amount to “MEDDLING” to the detriment of Republicans in this year’s midterm elections.

Giuliani has previously said that Trump has done nothing improper and is eager to talk to Mueller. On Tuesday, though, he said, he doesn’t want to make a call on whether Trump will sit down for an interview “until they decide whether they are going to give us the documents or not.”

Under pressure from the White House and congressional Republicans, the Justice Department last week held an unusual pair of briefings for lawmakers on the FBI’s use of the source, whom Trump has repeatedly cast as a “spy” implanted in his campaign.

There is no evidence to suggest that the source, former University of Cambridge professor Stefan A. Halper, was inserted into the campaign, as the president has suggested, but he did seek out and meet several Trump campaign advisers.

Giuliani said Tuesday that Mueller’s team has indicated that an interview would be a final step in the investigation. “They reserved the possibility they might have to interview a few people as a follow up,” he said. “But they said they had pretty much finished. This was four weeks ago.”

“I don’t think they would have asked to interview him until they are pretty much finished with everything,” Giuliani said. “They’re only going to get one shot at him. They know that. You look pretty amateurish if you interview him and you don’t have all the facts gathered.”

A spokesman for Mueller declined to comment.

Asked why Trump has spent so much time attacking the Mueller probe — the president has fired off a dozen tweets in recent days — Giuliani said the tactic is working.

“As an effective politician, you’re not going to do something that you don’t think is working,” Giuliani said.

He continued: “Spygate — that’s the reason — he’s not just ratcheted it up for no reason. He believes it is working, and he is genuinely upset about it.”